The present invention relates generally to a feeder for feeding mail related items such as mail insert materials, envelopes or mailpieces and, more specifically, to a retarding element in a friction feeder for preventing multiple feeds.
Friction feeders are known in the art. As the name suggests, a friction feeder relies on the interaction of several components around the exit nip of the feeder that results in the singulation of paper documents in a paper stack. The common components in most friction feeders are the driving mechanism to drive a sheet of paper document out of the exit nip and the retarding element to retain all the other sheets in the stack so as to prevent multiple feeds. To provide the necessary friction for retaining the other sheets in the stack, the surface of the retarding element is usually made of an elastomeric material or a hard, rough coating. Ifkovits, Jr. et al. (U.S. Pat. No. 5,294,102, hereafter referred to as Ifkovits) discloses a friction feeder wherein the surface of the retarding element is coated with tungsten carbide grit. Godlewski (U.S. Pat. No. 4,666,140) discloses a friction feeder wherein the surface of the retarding element is made of an elastomeric-like material. Green (U.S. Pat. No. 5,244,198) discloses a friction feeder wherein the retarding element is a continuous belt made of an elastomeric material mounted on a pair of rollers. A friction feeder can be designed to operate as a top feeder or a bottom feeder. The above-mentioned friction feeders are bottom feeders, wherein the sheets in a generally vertical stack are moved out the stack, one at a time, by a driving mechanism below the stack. A typical friction feeder is shown in FIG. 1. As shown, the feeder 1 uses a driving mechanism 30 to drive the bottom sheet 10 of a stack 20 out of the exit nip 64 and a retarding element 40 (a cylindrical member) to hold back the other bottom sheets. In general, the retarding element 40 has a relatively large diameter at the exit nip so that a number of sheets at the bottom of the stack can fan out to follow the surface curvature of the retarding element, forming a singulated stack portion 24. In the singulated portion, the sheets are slightly separated from each other in that the leading edge of one sheet is positioned slightly ahead of the sheets above. As shown in FIG. 1, the driving mechanism 30 comprises a continuous belt 32 mounted on a pair of rollers 34. However, the driving mechanism can simply be rollers with a resilient surface.
In order for the retarding element 40 to be effective in preventing other bottom sheets from being pulled out by the driving mechanism 30 along with the bottom sheet 10, the retarding element 40 must have a high friction surface 50 which is stationary relative to the moving sheet 10. The friction between the bottom sheet 10 and the sheet 10xe2x80x2 above is lower than the friction between the retarding surface 50 and a sheet 10xe2x80x2. If the surface 50 of the retarding element 40 is coated with a layer of hard grit, as disclosed in Ifkovits, paper dust will accumulate at the surface section 52 at the feed zone 62 where the sheet 10xe2x80x2 is retained by the retarding element 40 when the bottom sheet 10 is driven out and when the sheet 10xe2x80x2 itself is subsequently driven out of the exit nip 64. After extensive use, the surface roughness is reduced mainly because of the accumulated paper dust, thereby reducing the effectiveness of the retarding surface 50. If the surface 50 of the retarding element 40 is made of an elastomeric material, as disclosed in Green and Godlewski, the contact between the sheets and the retarding surface 50 at the feed zone 62 will wear out the contact surface section 52, changing the retard characteristics of the elastomeric surface.
In order to provide an unworn portion of the retarding surface to the exit nip, Green uses a locking mechanism to keep the retarding surface stationary in operation. When it is necessary to rotate the retarding surface to provide an unworn portion at the exit nip, the operator loosens the locking mechanism and manually repositions the retarding surface. This manual method of furnishing an unworn portion of the retarding surface is sporadic and inconvenient. Furthermore, the method requires the feeder to be removed from operation in order for the operator to reposition the retarding surface.
Thus, it is desirable and advantageous and desirable to provide a simple yet effective method and device for repositioning the retarding element in order to expose a fresh retarding surface in the feed zone of a friction feeder.
It is an objective of the present invention to provide a simple yet effective method and device to automatically furnish an unworn portion of the retarding surface in a friction feeder while the feeder is in operation. This objective can be achieved by using a cylindrical retarding member, which is allowed to rotate freely in one direction along its rotational axis but is prevented from rotating in the other direction. The retarding member is caused to rotate against the feeding direction of the friction feeder by a pre-determined amount after or before a sheet is driven out of the exit nip.
Accordingly, the first aspect of the present invention is a retard mechanism in a feeder for releasing generally flat items from a stack, the feeder having a driving mechanism capable of moving in a driving direction for releasing one flat item at a time through an exit point, with the leading edge of said one item exiting the exit point in an exiting direction on a singulation plane, wherein the retard mechanism is positioned relative to the exit point to prevent other flat items in the stack adjacent to said one flat item from being drawn out of the exit point by a first frictional force between adjacent flat items while said one flat item is exiting the exit point, said retard mechanism comprising a frictional surface having a surface section positioned at the exit point facing the singulation plane so as to allow the frictional surface to provide a second frictional force to the other flat items for overcoming the first frictional force. The retard mechanism comprises:
a cylindrical member having a curved surface to engage with at least said surface section of the frictional surface, the cylindrical member rotabably mounted on a rotation axis for rotation such that the cylindrical member is capable of rotating in a first rotating direction for causing said surface section to move away from the exit point in a direction opposite to the exiting direction so as to allow a different surface section of the frictional surface to move into the exit point; and
a motion restricting mechanism, operatively connected to the cylindrical member, for preventing the cylindrical member from rotating in a direction opposite to the first rotating direction, wherein
the driving mechanism is adapted to move in a retracting direction opposite to the driving direction in an intermittent manner so as to move at least one of the other flat items in a direction opposite to the exiting direction, thereby causing the cylindrical member to intermittently rotate in the first rotating direction by the second frictional force. The driving mechanism moves in the retracting direction prior to said one flat item being released or after said one flat item has exited the exit point.
Preferably, the frictional surface is fixedly attached to the cylindrical member or is an integral part of the cylindrical member.
Preferably, the frictional surface is made of a resilient material.
Alternatively, the frictional surface comprises a layer of hard grit.
The second aspect of the present invention is a feeder for releasing generally flat items from a stack. The feeder comprises:
a driving mechanism capable of moving in a driving direction for releasing one flat item at a time through an exit point, with the leading edge of said one flat item exiting the exit point in an exiting direction on a singulation plane, and
a retard mechanism, positioned relative to the exit point to prevent other flat items in the stack adjacent to said one flat item from being drawn out of the exit point by a first frictional force between adjacent flat items while said one item is exiting the exit point, wherein the retard mechanism comprises:
a frictional surface having a surface section positioned at the exit point facing the singulation plane so as to allow the frictional surface to provide a second frictional force to the other flat items for overcoming the first frictional force,
a cylindrical member having a curved surface to engage with at least said surface section of the frictional surface, the cylindrical member rotabably mounted on a rotation axis for rotation such that the cylindrical member is capable of rotating in a first rotating direction for causing said surface section to move away from the exit point in a direction opposite to the exiting direction so as to allow a different surface section of the frictional surface to move into the exit point; and
a motion restricting device, operatively connected to the cylindrical member, for preventing the cylindrical member from rotating in a direction opposite to the first rotating direction, wherein
the driving mechanism is adapted to move in a retracting direction opposite to the driving direction in an intermittent manner so as to move at least one of the other flat items in a direction opposite to the exiting direction for causing the cylindrical member to intermittently rotate in the first rotating direction by the second frictional force
The generally flat items can be sheets of paper, paper documents, mailing envelopes or mailpieces.
The third aspect of the present invention is a method of improving a retarding action of a retarding mechanism in a feeder for releasing generally flat items from a stack, the feeder comprising a driving mechanism capable of moving in a driving direction in order to release one flat item at a time through an exit point, with the leading edge of said one flat item exiting the exit point in an exiting direction on a singulation plane, wherein the retard mechanism is positioned relative to the exit point to prevent other flat items in the stack adjacent to said one flat item from being drawn out of the exit point by a first frictional force between adjacent flat items while said one flat item is exiting the exit point, wherein the retard mechanism comprises:
a frictional surface having a surface section positioned at exit point facing the singulation plane to provide a second frictional force to the other flat items for overcoming the first frictional force, and
a cylindrical member having a curved surface to engage with at least said surface section of the frictional surface, the cylindrical member rotabably mounted on a rotation axis for rotation such that the cylindrical member is capable of rotating in a first rotating direction for causing said surface section to move away from the exit point in a direction opposite to the moving direction of said one flat item so as to allow a different surface section of the frictional surface to move into the exit point.
The method comprises the steps of:
preventing the cylindrical member from rotating in a direction opposite to the first rotating direction, and
moving the driving mechanism in a retracting driving direction opposite to the first driving direction in an intermittent manner so as to move at least one of the other flat items in a direction opposite to the exiting direction, thereby causing the cylindrical member to intermittently rotate in the first rotating direction by the second frictional force.
The fourth aspect of the present invention is a retard element to be engaged with a retard mechanism in a feeder for releasing generally flat items from a stack, the feeder having a driving mechanism capable of moving in a driving direction for releasing one flat item at a time through an exit point, with the leading edge of said one item exiting the exit point in an exiting direction on a singulation plane, wherein the retard mechanism is positioned relative to the exit point to prevent other flat items in the stack adjacent to said one flat item from being drawn out of the exit point by a first frictional force between adjacent flat items while said one flat item is exiting the exit point. The retard element comprises:
a frictional surface, and
a cylindrical member having a curved surface to engage with at least a surface section of the frictional surface, the surface section positioned at the exit point facing the singulation plane so as to allow the frictional surface to provide a second frictional force to the other flat items for overcoming the first frictional force, wherein the frictional surface has a plurality of cuts in a generally helical or partially helical pattern.